UKM-SUM24-PG56+58_Layout 1 27/06/2024 11:35 Page 56


ELECTRONICS


may have a core of a material that increases the strength of the magnetic field. A change in the electric current flowing through an inductor creates a magnetic field that acts to inhibit that change in current. The field is proportional to the rate of change of the current, which means that fast-changing signals are inhibited more than slow-changing currents. In other words, the inductor acts as a filter, blocking higher-frequency signals. Inductors used in this way are often called chokes. Inductors are essential for many different circuit applications. Through their versatility you’ll find inductors in everything from IoT sensors to electric vehicle drive chains. They are typically low-cost components, but ship in huge numbers – the worldwide market for inductors is projected to grow from $5.1 billion in 2022, to $7 billion by 2027 .


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HOW DOES AN INDUCTOR WORK? When the changing electric current in an inductor produces a magnetic field, this stores energy in the field. The strength of the magnetic field flux, and hence the amount of energy stored, depends on multiple factors, including the size and shape of the inductor, the number of turns of wire in the coil, and whether it has a solid core. A ferromagnetic material such as iron can greatly increase the field strength.


The ratio between the magnetic flux linkage, ΦB, and the current, I, is defined as the inductance, L, of a particular component, as follows:


Figure 1: Bourns 04770x common--mode choke. (Source: Mouser Electronics)


Where, N = number of turns in the coil,


ΦB = magnetic flux and I is the current flowing through the coil.


As the magnetic field varies with time, it induces an electromotive force (EMF), or voltage, in the wire coil. Lenz’s law says that the direction of this voltage will act to inhibit the change of current. Faraday’s law of induction tells us that the


magnitude of the voltage induced, ε, is proportional to the rate of change of the magnetic field:


relationship between current and voltage without needing to derive any values for the magnetic field itself.


When the current through the coil stops changing and is held constant, the induced voltage therefore drops to zero. The magnetic field still stores potential energy. The unit of inductance is the henry (H), and induction values in commonly used components range from 1µH to 10H and beyond.


Rearranging this equation and substituting L from our first equation, we find that:


And we can calculate the voltage as follows:


An actual inductor will not, of course, exactly follow this theoretical behaviour of an ideal inductor. Other factors to consider include the resistance of the wire and parasitic capacitance between the turns of wire in the coil.


INDUCTOR USE CASES


This means that if we know the inductance of a component, we can calculate the


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Inductors find a wide range of use cases across many different industries. One of the most important general uses is filtering in power supplies to remove high-frequency noise and ripple. The inductor, or choke, acts as a low-pass filter, allowing the DC current to pass while blocking higher


n inductor is a passive component that stores energy in a magnetic field. It typically consists of a coil of wire connected to two terminals. The wire is insulated to avoid short circuits, and the coil


FUNDAMENTALS OF INDUCTORS


An inductor is one of the basic building blocks of an electronic circuit, but it can be overlooked or misunderstood by design engineers. In this article, Mouser Electronics’ Mark Patrick explains the essential basic theory behind how inductors work, their applications, and the different types of construction.


frequencies. A specific use case is blocking noise in differential pairs of power or data cables, where common-mode chokes remove the common-mode noise that is induced in the cables.


This high-frequency filtering is important to reduce electromagnetic interference (EMI) and to meet the standards for electromagnetic compatibility (EMC); without this filtering, products cannot legally be sold.


In automotive applications, the challenge of EMI is increasing due to the increasing number of electronic modules and systems within vehicles. This means there are more switching power supplies and, therefore, more EMI that must be mitigated.


Another use for inductors is to combine them with capacitors to create an LC circuit or LC filter, also known as a resonant or tuned circuit. The simplest LC filter uses one inductor (L) and one capacitor (C). Adding more components can improve performance in blocking unwanted frequencies. An LC circuit can also be used as a bandpass filter, which allows only signals in a specific frequency range to pass.


Inductors’ ability to store energy for short periods of time means they can be useful in DC/DC convertors; combining multiple inductors with a shared magnetic field is the basis of creating transformers. Inductors are also used in relays and switchgear, where the magnetic field causes


Figure 2: Abracon ASPI-F4030 and ASPI- F6060 molded SMD power inductors. (Source: Mouser Electronics)


Continued on page 58... Summer 2024 UKManufacturing


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